It is increasingly common for people to use client-side devices to communicate via a radio access network (RAN) with other devices, whether those devices are directly connected to the same RAN or to another network (such as another RAN or a transport network, as examples) to which that RAN directly or indirectly provides access. These client-side devices are generally referred to herein as access terminals, though this term is intended to broadly encompass devices known as mobile stations, user equipment, mobile devices, wireless-communication devices, cell phones, smartphones, personal digital assistants, tablets, laptops, air cards, Universal Serial Bus (USB) dongles, and/or any other device or combination of devices capable of functioning as an access terminal according to this disclosure.
Typically, the wireless communications that are sent from the RAN to one or more access terminals are described as being sent on the “forward link,” while those wireless communications that are sent from one or more access terminals to the RAN are described as being sent on the “reverse link.” These communications are typically formatted in accordance with a wireless-communication protocol, one example type of which is known as Code Division Multiple Access (CDMA). Moreover, CDMA networks that operate according to industry specifications such as IS-95 and IS-2000 are often referred to as 1xRTT (or just “1x”) networks, where 1xRTT stands for “Single Carrier Radio Transmission Technology.”
Furthermore, some RANs operate according to a particular type of CDMA protocol known as EV-DO (“Evolution Data Optimized”). These RANs are generally configured to operate according to one or more versions of industry specification IS-856, and are designed to provide high-rate packet-data service, including Voice over Internet Protocol (IP) (VoIP) service, to access terminals using a technique that is known as time-division multiplexing (TDM) on the forward link and what is essentially 1x-CDMA technology on the reverse link.
More generally, RANs can be configured to operate according to any of numerous other wireless-communication protocols, some examples of which are WiMAX (IEEE 802.16), Long Term Evolution (LTE), time division multiple access (TDMA), Global System for Mobile Communications (GSM), Wi-Fi (IEEE 802.11), and the like. Furthermore, some (“hybrid”) access terminals are equipped and arranged to be able to communicate according to multiple wireless-communication protocols (e.g., 1×CDMA and EV-DO).
In RANs that are of a type often known as wireless wide area networks (WWANs) (or cellular wireless networks), the entities with which access terminals communicate over the air interface are known by terms such as “base stations” and “access nodes,” among others. These terms are sometimes used in different ways to refer to different entities. For example, the term “base station” is sometimes used to describe simply a device known as a base transceiver station (BTS), which contains the hardware, antennas, and so forth that actually conduct the over-the-air portion of the communication with the access terminals on behalf of the RAN. At times, however, the term “base station” or “access node” is used to refer to a combination of (i) one or more BTSs and (ii) a device known as a “base station controller” (BSC) (or “radio network controller” (RNC)), which controls the BTS(s) and connects it (them) to the rest of the network.
In a typical scenario, an access terminal registers with a RAN via a particular BTS, and then operates in what is known as “idle mode” on a carrier frequency in a coverage area (e.g., a sector) provided by that BTS. If the access terminal is attempted to be contacted by another telephone, computer, or other communication device, the RAN will typically send the access terminal a page message via at least that particular BTS. The access terminal would typically respond by requesting and establishing communication on what is known as an air-interface traffic channel (or simply a “traffic channel”) and then conduct the relevant communication. In other instances, the access terminal is the initiator (perhaps when its user requests a webpage), in which case the access terminal sends the RAN an access-request message in order to request and establish communication on a traffic channel and then conduct the relevant communication.
Traffic channels take different forms under different types of air-interface protocols. In TDMA networks, traffic channels typically take the form of one or more timeslots of a repeating waveform on a carrier frequency used by multiple access terminals. In other words, in TDMA networks, different access terminals on different traffic channels take turns using the full transmit power of the base station at different times. In CDMA networks by contrast, different access terminals on different traffic channels simultaneously share the transmit power of the base station. In such networks, different traffic channels are delineated by the RAN applying different codes to different channels. These codes are generally known as spreading codes, and one commonly used type of spreading codes are known as Walsh codes.
Furthermore, there are multiple different types of spreading codes, perhaps best described by the relationship of the codes to one or more other codes. Some spreading codes are of a type known as fully-orthogonal spreading codes. As known in the art, when multiple spreading codes are simultaneously used in a sector on a carrier to delineate multiple traffic channels, none of the communications on any of those traffic channels will interfere with the communications on any other of those traffic channels if the spreading codes that are used are fully-orthogonal with respect to one another. If, however, the spreading codes are only quasi-orthogonal with respect to one another, then interference to some degree can and often will occur. Thus, fully-orthogonal spreading codes are typically preferred to quasi-orthogonal spreading codes, though, all else being equal, a lower maximum capacity can be realized using the former as opposed to the latter.